Conventional transfer control protocol (TCP) buffering management techniques do not detect congestion until after the congestion has occurred. The conventional TCP buffering techniques allow data packets to be discarded automatically (i.e., first-in-first-out buffer overflows) with no indication or signal presented to the sender to slow down or to resend discarded data packets. Hence, data packet congestion avoidance is not performed.
To keep the client/server nature of the conventional TCP as functional as possible, flow control is implemented. Features of the conventional TCP flow control include slow start, fast retransmit, and fast recovery. With the slow start feature, the conventional TCP is allowed to send new data packets to the network at the same rate at which it receives acknowledgments from the other end of the connection.
To accommodate the slow start, a window called a congestion window is added to the conventional TCP of a sender. Given an exponentially increasing nature of the congestion window, problems are bound to occur. Eventually the size of the congestion window will become large, congestion will occur, and segments carrying the data packets can be lost or dropped by intermediate devices, such as routers.
The fast retransmit process is used by the conventional TCP when a segment is believed to be lost in transmission. The conventional TCP specifies that all segments must be acknowledged. Thus, duplicate acknowledgments are sent when a segment is received out of order or possibly lost. A disadvantage of the conventional TCP is that there is no way of knowing whether the segment was lost in transmission or just received on the other end out of order.
The fast recovery process is used after the fast retransmit is implemented. The conventional TCP recalculates the congestion window size and performs a slow start operation. One particular problem with the fast recovery process is that any ongoing conventional TCP connection between two computers will still have data moving across the connection. If the computers need to stop what they are doing in order to reinstitute a slow start operation, eventually a severe performance degradation within the connection will occur.